1. Field of the Invention
The present invention relates to the isomerization of 2-methyl-3-butenenitrile into linear pentenenitriles, in particular into 3-pentenenitrile.
2. Description of the Prior Art
During the hydrocyanation of butadiene, in the presence of a nickel-based catalyst and an aryl phosphite co-catalyst, as described in U.S. Pat. No. 3,496,215, in addition to the 3-pentenenitrile target compound, a large amount of 2-methyl-3-butenenitrile is formed.
The latter compound cannot be directly used for the preparation of adiponitrile, one of the basic starting materials for the preparation of polyamide 66.
However, the amounts of this byproduct are so great, taking account of the vast tonnage of adiponitrile produced, that it is inconceivable to simply discard same to waste.
Also, it has long been a desideratum in this art to isomerize 2-methyl-3-butenenitrile into 3-pentenenitrile, an adiponitrile intermediate.
Thus, U.S. Pat. No. 3,536,748 describes converting 2-methyl-3-butenenitrile into linear pentenenitrile, by contacting same with a nickel-based catalyst of oxidation state 0, such as a tetrakis(alkyl or aryl phosphite)nickel, at a temperature of 10.degree. to 200.degree. C.
From the results obtained employing this isomerization process, it is observed that the percentage of linear pentenenitrile produced is very low, generally ranging from 0.4% to approximately 14% according to the examples of the patent, even though the reaction is carried out for several hours.
U.S. Pat. No. 3,676,481 describes an improvement to the above isomerization process, by using a promoter for the nickel catalyst, i.e., either a boron derivative or a salt of a metal of Groups Ib, IIb, IIIa, IIIb, IVa, IVb, Vb, VIb, VIIb and VIII of the Periodic Table, in particular the halides of these metals. This reaction is carried out in a homogeneous organic phase, which makes the separation of the reaction products and the catalyst difficult insofar as the recycling of the catalyst is concerned, which is always desirable.